Pyrotechnic igniter

ABSTRACT

An electrically actuated pyrotechnic igniter having its initiating or first-fire charge and bridge wire located adjacent the output end of the igniter with the main or sustaining charge positioned rearwardly thereof and providing prolonged flame output.

United States Patent [72] Inventors John D. Hawley East Hartland; William M. Smith, Simsbury, Conn. 21 App]. No. 773,808 [22] Filed Nov. 6, 1968 [45] Patented Mar. 16, 1971 [73] Assignee The Ensign-Bickford Company Simsbury, Conn.

[54] PYROTECHNIC IGNITER 7 Claims, 1 Drawing Fig. [52] U.S. Cl. 102/28 [51] Int. Cl F42b 3/12 [50] Field ofSearch 102/28, 49.7, 70.2; 60/(35.6 (RS)) Primary Examiner-Verlin R. Pendegrass Attorney-Prutzman, Hayes, Kalb & Chilton ABSTRACT: An electrically actuated pyrotechnic igniter having its initiating or first-fire charge and bridge wire located adjacent the output end of the igniter with the main or sustaining charge positioned rearwardly thereof and providing prolonged flame output.

Patented March 16, 1971 3,570,403

INVENTORS JOHN D. HAWLEY WILLIAM M. SMITH ATTORNEYS rrno'rncnurc rcurrnn BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates generally to pyrotechnic ignition devices and is particularly concerned with a new and improved ignition device of the electrically actuated type. lleretofore electrically actuated pyrotechnic igniters have been constructed with substantially the same configuration as electrically actuated explosive detonators. In both types of devices a pair of lead wires extend through a suitable base and are joined by a bridge wire located adjacent the base. An initiating or first charge positioned adjacent the base embeds the bridge wire while the main or sustainer charge of the device is located immediately in front of the initiating charge and at the output end of the device. The entire assembly is encased in a suitable covering such as a metal tube or shell. In the explosive detonator the main charge usually consists of primary and secondary explosive charges which are compacted forwardly of the initiating charge, while in the electric igniters the main charge is a similarly located pyrotechnic material frequently employed in the form of a centrally apertured pellet.

in operation an electric current is applied across the terminals of the device, causing the bridge wire to ignite the initiating or first charge. The ignited first charge sets off the main or sustainer charge of the device which in turn ruptures the casing and provides the desired short duration output.

Although the conventional configuration of internal components operates effectively for electrically actuated explosive detonators it tends to create performance problems when used in pyrotechnic igniters. In the case of an explosive detonator the initiating and main explosive charges function substantially instantaneously. However, the reaction time for burning of the initiating and main charges of the igniter is far slower, permitting the buildup or development of pressure within the device due to the confined position of the initiating charge between the base and the main charge. The pressure developed by the confined burning of the initiating charge results in a short duration output and can cause erratic functioning of the main charge. In addition, if the main charge does not ignite immediately the casing may rupture near the initiating charge and thus provide a flame output at the side of the device rather than at the end thereof. In either instance the output will be inconsistent and the performance of components downstream from the igniter could be affected.

Accordingly, it is an object of the present invention to provide a new and improved electric igniter having an arrangement of internal components which prevents development of a confined pressure area rearwardly of the main charge while providing a long duration flame output and increased reliability of operation.

Another object of the present invention is to provide a new and improved electric igniter of the type described having its initiating or first-fire charge located at the output end of the device thereby permitting immediate rupture of the casing and obviating erratic behavior associated with pressure buildup within the device rearwardly of the main charge.

Still another object of the present invention is to provide a new and improved electric igniter of the type described which positions the main pyrotechnic charge between the base of the device and the initiating charge to thereby effect rearward burning of the main charge and a long duration jet flame output which enhances reliable ignition of downstream pyrotechnic materials.

A still further object of the present invention is to provide a new and improved igniter of the type described which exhibits enhanced reliability, durability and efficiency coupled with ease of construction and simplicity of design.

Other objects will be in part obvious and in part pointed out more in detail hereinafter.

These and related objects are accomplished in accordance with the present invention by providing an electrically actuated pyrotechnic igniter having its initiating or first-fire charge and bridge wire located adjacent the output end of the igniter with the main or sustaining charge being positioned intermediate the initiating charge and the base of the device.

The invention accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth and the scope of the application which will be indicated in the appended claims.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a sectional view of an electric igniter constructed in accordance with the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT In the embodiment illustrated, the igniter is shown as a low voltage, hot wire initiator having an elongated cylindrical main body portion, generally designated by the reference numeral 12, with a pair of electrical terminals or posts 14 projecting outwardly from the rearward end thereof. The main body portion 12 of the igniter consists of a tubular sleeve or casing 16 extending substantially the full length of the igniter body and having a base plug or header 18 affixed in its rearward end 20. The exposed portions of a pair of electrical terminals l4 protrude from the base plug 18 which fully and effectively encloses end 20 of the tubular case 16 while at the same time providing a stable support for the electrically conductive posts 14 extending into the interior of the igniter. Advantageously the plug 18 can be made of any suitable support material. For example, it can be a hard rigid member such as glass, ceramic or the like, or a semirigid but firm member such as a rubber or plastic plug.

The rodlike posts 14 which generally are disposed in spaced a parallel relationship, do not extend entirely through the casing 16 but terminate adjacent the front or output end 22 of the device where they are joined or connected by a suitable resistance wire 24 commonly referred to as a bridge or hot" wire. While it will be appreciated that an exploding wire may be beneficially employed, a resistance wire will be described for purposes of illustration. The particular bird bridge wire utilized will vary depending upon the intended operating characteristics of the device. in this connection, it has been found that a wire of heavier gauge and longer length than has been conventionally employed heretofore, such as a wire exhibiting a resistance of about one ohm, gives satisfactory results.

Packed within the casing 16 between the header l8 and the bridge wire 24 is a main or sustainer charge 28. As shown, the main charge 23 preferably is placed within the sleeve 16 in abutting relationship to the base 18 and extends forwardly therefrom in a continuous manner along substantially the full interior length of the posts M. Accordingly, the main charge 2% terminates just short of the bridge wire connection between the poles l4 and may entirely fill the casing cavity in that area or take other forms such as a compressed sleeve which permits the poles 14 to extend through a central aperture of the charge. Positioned immediately in front of the main charge 28 within the tubular casing 16 is a first or initiating charge 30 which contacts and preferably embeds the resistance or bridge wire 24. The front face of the main charge 28 may be separated slightly from the confronting rear face of the first fire charge 3th by a fine mesh or paper disc 32 without interfering with the ability of the front charge Ell to positively and reliably ignite the pyrotechnic mix of the main charge. Advantageously the initiating charge Bil is compacted against the bridge wire 2- in the form of a heat sensitive disc or plug which is readily ignited by the heated wire. A shell or enclosure 42 circumscribes the sleeve 16 along substantially its entire length and is welded thereto adjacent the header 1?: in order to ensure full and complete encapsulation of the pyrotechnic charges. As shown, the shell 42; includes a front wall portion 44 of lesser thickness than the remainder of the shell to permit rupture thereof by the first charge Bill. The shell can be constructed of any suitable material although metal is generally preferred. Where stainless steel is employed it is sometimes necessary to have a front wall portion 44 having a thickness of 0.00l-0.002 inches. However, aluminum shells are also used advantageously.

As will be appreciated the length and type of both the initiating charge and the main output charge may be varied in order to control the duration of flame output from the igniter. However, in accordance with the present invention, the main charge 28 is usually of greater length, being at least twice the length of the first-fire charge. For example, in the particular igniter illustrated in the drawing the ratio is to l withthe main charge occupying about one-half the total length of the device while the initiating charge extends along only about one-twentieth of the total length of the igniter.

Generally, pyrotechnics have been found most effective for both the initiating charge and the main charge of the igniter, the combustible pyrotechnic material being mixed with a suitable amount of binder in order to provide the desired consistency for efficient manufacture of the respective charges. For example, the initiating pyrotechnic mix which must exhibit the appropriate heat sensitivity for ignition by the bridge wire, may beneficially comprise. a mixture of boron and lead oxide or zirconium and potassium perchlorate with a vinyl alcohol acetate resin binder. It is also within the scope of the present invention to use a primary explosive as the initiating charge to open the front wall portion 44 of the shell. On the other hand, the main charge illustratively comprises an aluminum, titanium, potassium perchlorate mixture with a resin binder and a minor amount of an additive or stabilizer effective in slowing down the reaction to provide the desired period of sustained flame output and to improve long term stability. For example, with a bridge wire of 1 ohm resistance and the perchlorate pyrotechnic mixes mentioned hereinbefore, the igniter may exhibit an ignition time of approximately 35 milliseconds with a direct current of 6 amperes at 26 volts and a sustained output for over 1 second. Using a mixture of boron and lead oxide in place of the zirconium, potassium perchlorate mix provides a reaction time of 20 milliseconds at l ampere and 28 volts.

In accordance with the present invention, the period of flame output should exceed the millisecond range of prior devices and last for a period of at least 1 second or more in order to provide the most effective results. In this way the device provides a sustained jet of flame similar to that of a blowtorch, thereby decreasing the possibility of unsuccessful operation of the igniter.

As will a be appreciated, the application of current to the bridge wire 24 through the poles 14 causes the bridge wire to heat sufficiently to ignite the pyrotechnic or explosive first charge 30. This initial ignition will cause rupture of the front wall portion 44 of the shell 42 thus preventing a further buildup of pressure within the device. Simultaneously the first charge ignites the main pyrotechnic charge which is then free to burn rearwardly toward the base or header 18, causing a jet of flame to be projected forwardly from output end 22 for a period of greater than 1 second.

As will be apparent to persons skilled in the art, various modifications and adaptations of the structure above described will become readily apparent without departure from the spirit and scope of the invention.

We claim:

1. An electrically actuated closed pyrotechnic igniter comprising a tubular casing having front and rear ends, a rupturable front wall enclosing the front end of the casing, a first charge positioned within the casing at the front end thereof in confronting relationship with the front wall for rupturing said wall and discharging its combustion products forwardly of the casing upon ignition, a main charge positioned rearwardly of the first charge and adjacent thereto for ignition by the first charge, a bridge wire in contact with the first charge for ignition thereof upon receipt of an electrical signal and electric signal-conductin means connected to the bridge wire and extending rearwar y therefrom along the casing for conveying the electrical signal to the bridge wire.

2. The igniter of claim 1 wherein the main charge includes a pyrotechnic material and is capable of producing a sustained flame output.

3. The igniter of claim 1 wherein the main charge is an elongated mass extending longitudinally of the casing for rearward burning upon ignition by the first charge and forward discharge of a jet of combustion products.

4. The igniter of claim 1 including a base member affixed to the casing rearwardly of the main charge, the electric signalconducting means being supported by the base member and providing electrical terminals projecting outwardly from the casing.

5. The igniter of claim 4 wherein the electric signal-conducting means include a pair of posts secured to the base and extending forwardly thereof through the main charge, the posts terminating adjacent the forward extremity of the main charge.

6. The igniter of claim 1 including a confining outer shell secured to the tubular casing and a base member enclosing the rear end of the casing, said shell securing the rupturable front wall in confronting relationship to the first charge for rupture thereby upon ignition, the main charge being confinably and contiguously positioned between the base member and the first charge for rearward burning toward the base member upon ignition by the first charge, the flame output of the ignited main charge extending forwardly of the casing.

7. The igniter of claim 1 wherein the first charge is a solid plug filling the front end of the casing and separating the main charge from the rupturable front wall. 

1. An electrically actuated closed pyrotechnic igniter comprising a tubular casing having front and rear ends, a rupturable front wall enclosing the front end of the casing, a first charge positioned within the casing at the front end thereof in confronting relationship with the front wall for rupturing said wall and discharging its combustion products forwardly of the casing upon ignition, a main charge positioned rearwardly of the first charge and adjacent thereto for ignition by the first charge, a bridge wire in contact with the first charge for ignition thereof upon receipt of an electrical signal and electric signal-conducting means connected to the bridge wire and extending rearwardly therefrom along the casing for conveying the electrical signal to the bridge wire.
 2. The igniter of claim 1 wherein the main charge includes a pyrotechnic material and is capable of producing a sustained flame output.
 3. The igniter of claim 1 wherein the main charge is an elongated mass extending longitudinally of the casing for rearward burning upon ignition by the first charge and forward discharge of a jet of combustion products.
 4. The igniter of claim 1 including a base member affixed to the casing rearwardly of the main charge, the electric signal-conducting means being supported by the base member and providing electrical terminals projecting outwardly from the casing.
 5. The igniter of claim 4 wherein the electric signal-conducting means include a pair of posts secured to the base and extending forwardly thereof through the main charge, the posts terminating adjacent the forward extremity of the main charge.
 6. The igniter of claim 1 including a confining outer shell secured to the tubular casing and a base member enclosing the rear end of the casing, said shell securing the rupturable front wall in confronting relationship to the first charge for rupture thereby upon ignition, the main charge being confinably and contiguously positioned between the base member and the first charge for rearward burning toward the base member upon ignition by the first charge, the flame output of the ignited main charge extending forwardly of the casing.
 7. The igniter of claim 1 wherein the first charge is a solid plug filling the front end of the casing and separating the main charge from the rupturable front wall. 